High-pressure discharge lamps with a discharge vessel, for example made of ceramics, and a fill including sodium, mercury and a noble gas, are well known, see for example the referenced U.S. Pat. No. 4,633,135, Akins, the disclosure of which is hereby incorporated by reference. In lamps of this type, which have a very high light output per power unit, a starting or firing assistance is usually provided The starting or firing assistance usually takes the form of an elongated metallic element, such as a metal wire, strip or the like, placed against the outside of the discharge vessel. This wire is coupled to one of the electrodes. During operation of the lamp, and particularly upon extended operation, the wire may interact with the ceramics of the discharge vessel and lead to electrolysis, and the discharge vessel may then be destroyed. It has been proposed to place a bimetallic element between the current supply lead and the starting assistance strip or wire which, upon heating of bimetallic element after ignition, lifts the wire off engagement from the sodium high-pressure discharge vessel, and thus inhibits continued electrolysis.
The lamp finds continued use, primarily due to its high light output, and, since suitable combinations of the fill were found, the color characteristics of the lamp, also in part due to specific pressure relations therein, have been so improved that the lamps are used for applications which, heretofore, had been reserved only for high-pressure discharge lamps with specifically designed high color rendering indices.
The referenced U.S. Pat. No. 4,633,135, Akins, describes a lamp of this type in which a bimetallic strip has one end secured approximately in the center of the auxiliary ignition strip, the other end of the wire being secured to a frame which is located within the outer bulb or enclosure, and extending parallel to the discharge vessel This frame structure substantially increases manufacturing costs, and further requires a lamp which is substantially larger than lamps which do not have such frames. Further, the frame makes the lamp non-symmetrical, and the non-symmetrical distribution of weight therein requires a single base of the lamp at one end. The frame structure does not permit building the lamp in double-ended form, so that it can be snapped into sockets, as is customary in tubular, double-ended lamps.